A circuit breaker is a special type of electrical switch, which is designed to protect other electrical circuitry from damage caused by an electrical fault, such as an overload condition, short circuit, or the like. In general, a circuit breaker allows current to pass from a power supply to load circuitry during normal operating conditions and will quickly react to prevent current from passing from the power supply to the load circuitry upon detection of a fault. Most circuit breakers incorporate a mechanical switch that controls the continuity between the power supply and the load circuitry. Under normal operating conditions, the mechanical switch is closed, and continuity is provided between the power supply and the load circuitry. When a fault is detected, the mechanical switch is opened, and continuity between the power supply and the load circuitry is electrically and mechanically broken. As such, the flow of current between the power supply and load circuitry is broken.
Circuit breakers are applied to both direct current (DC) and alternating current (AC) applications over extremely wide power ranges. Since circuit breakers are designed to be reset after being tripped in response to detecting a fault, the mechanical switches in the circuit breakers may be designed to be opened and closed many times. Depending on the application, the mechanical switch in the circuit breaker may need to be able to withstand hundreds, if not thousands, of openings and closings. As such, maintaining the integrity of the mechanical switch over numerous openings and closings is often a critical design requirement. However, numerous aspects of the mechanical switch and its operation tend to degrade the integrity of the mechanical switch with each opening and closing. For example, each impact that one contact makes against the other contact when the mechanical switch is closed may damage one or both of the contacts. The damage caused over numerous closings may degrade the performance of the mechanical switch or lead to a complete failure. Further, an arm or member that must move to place the contacts in and out of contact with one another when closing or opening may weaken or break over time, which may also lead to performance degradation or complete failure. To address these issues, designers are working to improve materials and the physical design of the mechanical switches.
Another destructive force that tends to degrade the integrity of a circuit breaker is the electrical arcing that occurs between the contacts of the mechanical switch before the contacts make contact with each other during closing of the mechanical switch, or after the contacts break contact with each other during the opening of the mechanical switch. When the voltage differential between contacts that are sufficiently close together is at a given level, an electrical arc is generated between the contacts. In essence, an electrical arc is the breakdown of a gas that resides between the contacts into a plasma. The resulting plasma in this instance is an ionized gas that tends to generate excessive current and heat at the points of arcing on the contacts. The heat from the arcing erodes the contacts, and over time, will also lead to performance degradation or complete failure of the mechanical switch, and thus the circuit breaker. The destructive effect of arcing increases as the voltages and currents handled by the circuit breaker increase.
Efforts have been made to replace the mechanical switches in the circuit breakers with semiconductor based switches to avoid the inherent issues associated with the mechanical switches. For high power applications, semiconductor solutions typically cannot compete with the voltage and current handling capability of a mechanical switch. Further, there are safety concerns with semiconductor switches not providing a clean and clear mechanical break, like that provided by mechanical switches, between the power source and the load circuitry.
Accordingly, there is a need for an efficient and effective circuit breaker that is capable of providing a mechanical break between the power source and the associated load circuitry while mitigating the contact erosion caused by plasma formation.